FIG. 11 is a schematic diagram showing the configuration of a laser oscillator. In FIG. 11, reference numeral 1 denotes a laser diode that emits light when a direct current is received from a power supply device 10; 2, denotes a laser medium; 3, a total reflection mirror; 4, a partial reflection mirror; 5, an expansion lens for expanding a laser beam; 6, a parallel shifting lens for changing a laser beam into parallel beams; 7, an optical fiber entrance lens; 8, an optical fiber; 9, a machine head; and 10, a power supply device.
By supplying a direct current to the laser diode 1, light is emitted, the laser medium 2 is excited, and resonance is generated between the total reflection mirror 3 and the partial reflection mirror 4. As a result, a laser beam is obtained.
The thus obtained laser beam is expanded by the expansion lens 5 and is changed into parallel beams by the parallel shifting lens 6, and the obtained beams are concentrated at the end face of the optical fiber 8 by the optical fiber entrance lens 7. Then, the concentrated laser beam passes through to the inside of the optical fiber 8 and is guided to a predetermined location through the machine head 9.
The laser output can be adjusted by varying the current supplied to the laser diode 1. Generally, a predetermined laser output or a current instruction is externally transmitted to the power supply device 10 that supplies current to the laser diode 1, and the power supply device 10 then controls the current that is to be supplied to the laser diode 1.
FIG. 12 is a diagram showing a specific internal example for the power supply device 10. First, the basic operation of the power supply device 10 will be described.
In the power supply device 10, input power is transformed into a direct current by a rectifier 16, and the direct current charges a capacitor 17.
Then, a transistor 13 is turned on, and a current begins to flow to the laser diode 1 through a reactor 14.
The amount of current flowing to the laser diode 1 is increased while the transistor 13 is on, and when the amount of the current exceeds a desired current value, the transistor 13 is turned off to decrease the current.
When the amount of the current falls below the desired current value, the transistor 13 is turned on to increase the current.
By repeating the turning on and off of the transistor 13, the amount of current is adjusted to obtain the desired current value.
An example on and off control process is, as is shown in FIG. 13, a hysteresis comparator control process wherein the ON and OFF states are controlled within a range extending from the upper to the lower limit current values that are provided, or a PWM control process wherein the ON time is controlled during a specific period of time.
The control process will now be described in detail while referring to FIG. 12.
A current controller 18 fetches a desired current value (current instruction value), and the value of a current that is obtained through a current sensor 12, that is appropriately controlled by a gain adjustment unit 20, and that is currently flowing.
In the hysteresis comparator control process, these two types of data are fetched by a comparator 21, and the comparator 21 compares the data with a current value for turning on the transistor 13 and a current value for turning off the transistor 13, both of which are set in advance, and determines whether the transistor 13 should be turned on or off.
Though not shown in FIG. 12, in the PWM control process a difference between the two types of data is calculated by a microcomputer, and the ON time is controlled within a specific period of time.
The thus obtained ON or OFF instruction of the transistor 13 is transmitted to a circuit for driving the transistor 13 (a circuit that, based on a logic signal received from a control system, supplies the current or the voltage actually required to turn the transistor 13 on or off). As a result, the transistor 13 is turned on or off.
Through these operations, the power controller 18 fetches a desired current value, and adjusts the current to match the desired current value.
The control process for obtaining a desired laser output value will now be described.
The power controller 18 fetches a desired laser output instruction value and a laser output monitor value (current laser output) that is transmitted through a laser output monitor sensor 11.
The power controller 18 calculates a difference between the obtained data, and adjusts a presently available current instruction value.
Based on the adjusted current instruction value, the transistor 13 is turned on or off in the same manner as when an externally supplied, desired current value is received.
A switch 19 is a selection switch used to validate a current instruction or a laser output instruction.
A solid-state laser oscillator, which is controlled as described above, is used for welding or cutting metal.
When a desired laser output can not be maintained, a welding failure or a cutting failure occurs. Thus, means is required for providing an external alarm warning that an abnormality has occurred when the desired laser output can not be maintained.
As example means for providing an external alarm when an abnormality has occurred and the desired laser output can not be obtained, for a minimum required laser output of 200 W, a circuit 25 is additionally provided that is turned on when the laser output monitor value reaches 200 W, and that transmits an ON signal to an oscillator controller 26. Further, awaiting period for the ON signal is defined, and when the signal is not rendered on within the allocated period of time, an abnormality notification is provided.
Further, in an example wherein an upper laser output limit is defined to prevent too much welding power, a maximum 300 W is set as the upper limit value, and a circuit 24 is additionally provided that is turned on when the laser output exceeds the upper limit. Using this ON signal, an abnormality notification can be provided.
In addition, a maximum available current is defined for the laser diode 1, and when a current equal to or greater than the defined value is supplied, an abnormality occurrence notification must be given externally.
When, for example, the laser diode 1 will be damaged when a current of 50 A or greater is supplied, a circuit 23 is additionally provided that is turned on when the current monitor value obtained by the current sensor 11 is greater than 50 A. This ON signal is transmitted to the oscillator controller 26 as an abnormality notification.
Based on this ON signal, the oscillator controller 26 performs an appropriate process (e.g., a power cutoff) and protects the laser diode 1.
An example arrangement for protecting the laser diode 1 has been explained. However, when the value of a current that can flow to another device, such as the transistor 13 or the reactor 14, is lower than the available value of a current flowing to the laser diode 1, the defined current value must be changed in accordance with the other device.
As is described above, since the solid-state laser oscillator has means for providing an external notification for a laser output abnormality, a welding or cutting failure can be prevented.
Furthermore, when a current flows that is equal to or greater than a defined value, the means for providing an external notification of an abnormality protects the individual devices.
When both an abnormality resulting from the laser output exceeding an upper limit and an abnormality resulting from a current value exceeding a defined value occur at the same time, the above described conventional solid-state laser oscillator can determine whether too much current has been supplied to the laser diode 1, and can also determine whether the laser output exceeded the upper limit because of the power supply abnormality.
A power supply abnormality is an abnormality other than one for the light amplification portion (damage to a PR mirror or a TR mirror) excluding the laser diode 1 in FIG. 1. An example abnormality is the failure of a device used to supply power.
However, merely by providing notification that an abnormality has resulted from the laser output exceeding an upper limit (an abnormality resulting from a current value exceeding a defined value has not occurred), whether there is a power supply abnormality can not be determined.
While referring to FIG. 12, an explanation will now be given for an example laser oscillator wherein the lower output limit value is 200 W, the upper limit value is 300 W, and the maximum defined current value is 50 A; wherein a laser output of 250 W is obtained when a current of 20 A is supplied, and a laser output of 350 W is obtained when a current of 40 A is supplied; and wherein a desired current instruction value is 20 A.
When 0.5 times an actual current value is returned to the comparator 21, as the current monitor value obtained by the current sensor 11, because an abnormality has occurred at the gain adjustment unit 20, (1/0.5) times a current, i.e., 40 A, is actually supplied to the laser diode 1, while a current of 20 A was originally transmitted to the laser diode 1. Therefore, a 350 W laser is output.
Thus, conventionally, it can be determined that an abnormality has occurred wherein the laser output exceeds the upper limit. At this time, since the current actually flowing across the laser diode 1 is 40 A, which is equal to or lower than the maximum defined current value, an abnormality that occurs when the current value exceeds the defined value is not detected.
Generally, an abnormality in a light amplification portion is assumed to be an abnormality that occurs when the laser output exceeds the upper limit. In this case, however, it should be determined that an abnormality has occurred, not at the light amplification portion but at the gain adjustment unit 20 of the current controller 18, i.e., that a power supply abnormality has occurred. This abnormality can not be precisely detected.
In addition, when wiring extended to the laser diode 1 is cut off, a current does not flow to the laser diode 1, and accordingly, no laser is output.
Therefore, the laser output is reduced, to below the lower limit, and a laser output abnormality occurs.
At this time, since a current does not flow across the laser diode 1, an abnormality resulting from the current value exceeding the defined value does not occur.
Also in this case, it should be determined that the abnormality has not occurred at the light amplification portion, but that the abnormality, i.e., a power cutoff, has occurred at the power supply portion. However, the power supply abnormality can not be designated merely by detecting the laser output abnormality.
This is because, since the detection of the power supply abnormality is performed in order to protect the power supply body (to protect devices such as the laser diode 1 and the transistor 13), a power supply abnormality that would cause a welding failure or a cutting failure is detected as the laser output abnormality.
That is, the conventional laser oscillator can detect the laser output abnormality to prevent the occurrence of a welding failure or cutting failure. However, whether the abnormality has occurred at the light amplification portion or the power supply portion can not be determined, for it is difficult to identify the location of the abnormality, and to cope with the abnormality, an extended period of time is required.